Development of a Double Pendulum for Gravitational Wave Detectors

TL;DR

This paper discusses the development of a double pendulum system as a test bed to improve seismic noise filtering in future ground-based gravitational wave detectors like LIGO.

Contribution

It introduces a dedicated apparatus for testing double pendulum designs, focusing on dynamic ranges, transfer functions, and noise characteristics relevant to gravitational wave detection.

Findings

Characterization of actuator dynamic ranges

Measurements of seismic transfer functions

Analysis of sensor and actuator noise

Abstract

Seismic noise will be the dominant source of noise at low frequencies for ground based gravitational wave detectors, such as LIGO now under construction. Future interferometers installed at LIGO plan to use at least a double pendulum suspension for the test masses to help filter the seismic noise. We are constructing an apparatus to use as a test bed for double pendulum design. Some of the tests we plan to conduct include: dynamic ranges of actuators, and how to split control between the intermediate mass and lower test mass; measurements of seismic transfer functions; measurements of actuator and mechanical cross couplings; and measurements of the noise from sensors and actuators. All these properties will be studied as a function of mechanical design of the double pendulum.